/*
 * Copyright (c) 2015 Typelevel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package alleycats

import cats.Hash

/**
 * A `Hash[A]` that delegates to identity hashcode (`System.identityHashCode`).
 * It implements `Eq[A]` via referential equality (`eq`) that it is not referentially transparent!
 */
trait SystemIdentityHash[A <: AnyRef] extends ReferentialEq[A] with Hash[A] {
  override def hash(a: A): Int = java.lang.System.identityHashCode(a)
}

object SystemIdentityHash {
  private[this] val identityHash: Hash[AnyRef] = new SystemIdentityHash[AnyRef] {}

  def apply[A <: AnyRef]: Hash[A] = identityHash.asInstanceOf[Hash[A]]
}
